Modern analytical instruments are particularly susceptible to performance variations due to the thermal sensitivity of certain components that operate within the analytical instrument. The temperature of one or more components of an analytical instrument is typically controlled by locating the component in a temperature-controlled environment, or thermal zone. The temperature of the thermal zone is typically, effected by an electrically-powered heating device or cooling device, or a combination of such devices.
One particular type of analytical instrument is a chromatograph. The basic components of a chromatograph include an injection port for introducing a sample of matter to be examined into a stream of carrier fluid, a separation column attached to the injection port that causes some of the constituents of the sample to elute at different times, and a detector for producing a signal indicative of the presence of the constituents being eluted. A signal processing section may be employed for integrating the signal so as to provide information as to the quantity of each constituent.
In the typical gas chromatograph, the temperature controlled zone is constructed as an oven. The injection port and detector are attached to respective pneumatic fittings on the oven housing, and the separation column, usually mounted on a basket, is attached between the pneumatic fittings and located within the oven. The oven housing typically comprises a door and an enclosure having several insulated oven housing walls. A heating element and a stirring fan located in the oven respectively heats and stirs the air contained within the oven housing so as to minimize temperature gradients therein that could adversely affect the performance of the chemical process occurring within the column. During a typical sample analysis, the heating element is operated so as to increase the temperature of the oven from a minimum initial value to a maximum final value. Before introduction of the next sample into the column, the temperature of the oven is usually returned to its initial value.
Accordingly, with repeated cycling of the heating unit, fan, and other such devices, a large amount of energy is generated and dissipated, and thus the chromatograph consumes a considerable amount of power.
Further, the chromatograph is sometimes constructed for simultaneous operation of more than one column located within the thermal zone. With additional columns, detectors, injectors, and related devices, this construction allows such a chromatograph to operate in a wide variety of different configurations and methods for sample analysis. However, a large oven cavity is required to accommodate the increased number of components. When the oven is operated with but one injector, column, and detector, a large proportion of the oven cavity is unoccupied and is unused. Nevertheless, the entire oven cavity is subject to the usual patterns of heating and cooling. The temperature control system also exhibits an oven temperature ramp rate that is less than desirable, i.e., the time required for heating and cooling the oven cavity is too long. The overall efficiency of the oven is, therefore, sub-optimal.
Accordingly, the conventional chromatograph is best suited for use in the laboratory, or similar settings, where sufficient space and electrical power are available. There have been attempts to reduce the size and complexity of a chromatograph so as to be practical outside of the laboratory. Such miniaturization has not been fully realized, due in part to the power demands put on the system by an inefficient oven, and due to the large size and large thermal mass that is presented by the typical oven housing.
There is, accordingly, an unresolved need for a compact, reliable, and efficient system for providing the requisite control of a thermal zone in an analytical instrument.